The present invention relates to an automatic gearbox having a control device for selecting a gearbox driving position.
In the case of automatic gearboxes for motor vehicles, it is conventional to transmit a motor vehicle driver""s requirement for a gearbox driving position, specifically with regard to a forward driving position V, a reverse driving position R, a neutral position N and a parking position P, to the automatic gearbox from a selector lever mechanically via a linkage. The linkage can be used to actuate a hydraulic spool valve via which consumers, in particular brakes and clutches for the individual gearbox driving positions, can be connected to pressure connections.
U.S. Pat. No. 5,409,434 describes a generic automatic gearbox of a control device for selecting a gearbox driving position. The control device has three hydraulic spool valves which can be actuated via electrically actuatable shift valves, as a result of which what is referred to as xe2x80x9cshift-by-wirexe2x80x9d gear-changing can be implemented. A selector lever can be replaced by electric switches, and a linkage by signal lines, enabling construction space, in particular, to be reduced and tolerances to be avoided.
It is an object of the present invention to provide an automatic gearbox having a control device for selecting a gearbox driving position and providing improved driving safety.
The present invention provides an automatic gearbox having a control device for selecting a gearbox driving position, which device includes at least one spool valve via which at least one pressure connection may be connected to at least one consumer, and having at least one shift valve via which at least one pressure connection from at least one pressure supply of the control device may be shifted to the spool valve in order to actuate the spool valve.
The control device may include a retaining device via which, if the shift valve should fail, the spool valve may be fixed in at least one control position and the selected gearbox driving position may be retained. If the control valve should fail, in the selected gearbox driving position, a motor vehicle may at least be moved from a hazardous location and the driving safety may be increased.
The retaining device may be implemented by various arrangements and may be implemented, for example, mechanically, electromechanically and/or electromagnetically. Additionally, the retaining device may be implemented hydraulically, enabling construction space, installation outlay and costs to reduced. This may be achieved in a particularly simple and cost-effective manner in terms of construction by a changeover valve, in particular a ball changeover valve, which, when the shift valve is activated, enables a pressure connection between the pressure supply of the control device and a pressure chamber on the spool valve, and, when the shift valve is subsequently deactivated, changes over and prevents a return flow from the pressure chamber.
A further example embodiment of the present invention provides an automatic gearbox having a control device for selecting a gearbox driving position, which device includes at least one first spool valve for a first gearbox driving position, for example for forward travel, and at least one second spool valve for a second gearbox driving position, for example for reverse travel, via which spool valves at least one pressure connection may be connected to at least one consumer, and having at least one shift valve for the first gearbox driving position and a shift valve for the second gearbox driving position, via which shift valves at least one pressure connection from at least one pressure supply of the control device may be shifted to the respective spool valve in order to actuate the spool valve.
The pressure connection, which may be shifted via the first shift valve, for the first gearbox driving position is conducted via the second spool valve and, when the second gearbox driving position is selected, the pressure connection for the first gearbox driving position is interrupted by the second spool valve. It may reliably be avoided that when the second gearbox driving position is selected a malfunction is simultaneously able to actuate the first spool valve and connect consumers, in particular brakes and clutches for the first gearbox driving position, to pressure connections via the first spool valve. The pressure connection, which may be shifted via the second shift valve, for the second gearbox driving position may be conducted via the first spool valve and, when the first gearbox driving position is selected, may be interrupted by the first spool valve. It may reliably be avoided that, when the first gearbox driving position is selected, a malfunction is able to simultaneously actuate the second spool valve and connect consumers, in particular brakes and clutches for the second gearbox driving position, to pressure connections via the second spool valve.
If the control device has a retaining device via which, if the shift valve should fail, the spool valve may be fixed in at least one control position and the selected gearbox driving position be retained, resetting of the spool valve and of the selected gearbox driving position may be achieved by an additional shift valve. However, the control device may include, in addition to the two spool valves for the two first gearbox driving positions, in particular for the forward driving position and the reverse driving position, at least one third spool valve for a third gearbox driving position, in particular the neutral position, which third spool valve may be actuated by simultaneous activation of the first and second shift valves and, as a result, a pressure connection may be produced for resetting the first and/or second spool valve. An additional shift valve for resetting the first and second gearbox driving positions and construction space and costs associated therewith may be reduced. A spool valve is less expensive than a shift valve and may be integrated in a hydraulic plate in a space-saving manner.
In a further example embodiment of the present invention, the shift valves are pulse-controlled, as a result of which energy usage may be reduced and wear may be reduced.
In order to actuate a parking brake, a relatively large force is required in comparison to an actuating force of the three spool valves (xe2x80x9cforwardxe2x80x9d, xe2x80x9creversexe2x80x9d, xe2x80x9cneutralxe2x80x9d). If the pressure supply of the control device is designed exclusively for selecting at least one forward driving position, at least one reverse driving position and/or a neutral position, this may be implemented at a low pressure level.
The parking brake may be actuated mechanically, electrically and/or electromagnetically. A separate spool valve and a separate pressure supply may be provided for the parking brake, as a result of which construction space, weight and installation outlay may be reduced. If at least one selected gearbox driving position may be reset by actuation of the parking brake, it may reliably be avoided that the parking brake is actuated and the forward driving position or the reverse driving position is selected at the same time.